This invention relates generally to a shear mixing apparatus and its use in various processes. This invention relates more particularly to a shear mixing apparatus that generates very small bubbles and to use of the apparatus to supply a gas to a liquid medium. This invention relates still more particularly to such an apparatus and its use to enhance mass transfer of a reactive gas in applications such as a chemical or biological reaction. One such reactive gas is oxygen.
M. Motarjemi and G. J. Jameson, in "Mass Transfer from Very Small Bubbles--The Optimum Bubble Size for Aeration", Chemical Engineering Science, Volume 33, pages 1415-1423 (1978), teach that bubbles are frequently used for mass transfer purposes, especially in systems where oxygen is dissolved in water. They suggest, at page 1422, a need for developing practical new ways to make "very small bubbles, less than 1 mm in diameter, in large quantities." G. J. Jameson, in "Bubbles in Motion", Trans IChemE, Vol. 71, Part A, pages 587-594 (November 1993), provides an overview of Professor John Davidson's contributions to the study of bubbles and gas-liquid two-phase flows. At page 592, he discusses problems inherent in generating small bubbles by reducing diffuser mean hole diameter. The problems include dramatic increases in pressure drop across the diffuser and potential blocking of the hole by solids present in bodies of water such as sewage ponds. At page 593, he discusses bubble coalescence and notes that it will be necessary to impart a force to bubbles in order to remove them quickly from the orifice to prevent coalescence. Possible means of imparting such a force include a fluid cross-flow over the orifice or an oscillation applied either to the orifice itself or to gas within the orifice.